feedback: VDE-115 -- missing wall_thickness and undercut_detection APIs; DFM+mold modules need these for manufacturability analysis

2026-07-31 08:19:56 +08:00
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+# VDE-115: VDE lacks wall thickness and undercut detection APIs; DFM module forced to manual geometry analysis
+
+**Date**: 2026-07-31
+**Severity**: High (DFM/mold design cannot use VDE for critical geometric checks)
+**Status**: Submitted
+
+## Summary
+
+The DFM checker module (`src/vd_mfg_dfm/dfm_checker.cpp`, 1129 lines) implements
+manufacturability analysis but cannot use VDE for two critical geometric analyses:
+
+| Capability | VDE Status | Impact |
+|-----------|-----------|--------|
+| Wall thickness analysis | **Missing** | 200+ lines manual code |
+| Undercut detection | **Missing** | 50+ lines manual code |
+
+Both are fundamental to DFM, mold design, and die casting analysis.
+Every major CAD platform provides these — we must request VDE to add them.
+
+## Wall Thickness Analysis
+
+### Manual Implementation in dfm_checker.cpp
+
+`checkWallThickness()` / `checkWallThicknessFromShape()` (lines 395-470, 851-923) perform:
+- Measure minimum wall thickness across the model
+- Compare against material-specific thresholds
+- Detect thin walls that would cause mold fill / structural issues
+- Sample points on surfaces and measure thickness along normals
+
+### Proposed VDE API
+
+```cpp
+// vde/brep/wall_thickness.h
+
+namespace vde::brep {
+
+enum class WallThicknessMethod {
+    RayCasting,      // Shoot rays from face into body → find opposite face
+    MedialAxis,      // Medial axis transform → skeleton-based distances
+    ClosestPoint     // KD-tree nearest point on opposite side
+};
+
+struct WallThicknessParams {
+    WallThicknessMethod method = WallThicknessMethod::RayCasting;
+    int sample_density = 50;       // samples per face in each param direction
+    double min_thickness = 0.5;    // alert threshold (mm)
+    double max_thickness = 50.0;   // max wall alert (sink marks)
+};
+
+struct WallThicknessPoint {
+    Point3D position;
+    Point3D opposite_point;    // point on opposite face
+    double thickness;
+    int face_index;
+    bool below_threshold;      // thinner than min_thickness
+};
+
+struct WallThicknessResult {
+    std::vector<WallThicknessPoint> samples;
+    double min_thickness;
+    double max_thickness;
+    double avg_thickness;
+    double stddev_thickness;
+    int thin_region_count;     // number of thin regions
+    int thick_region_count;
+    AABB3D bounding_box;
+};
+
+[[nodiscard]] WallThicknessResult analyze_wall_thickness(
+    const BrepModel& body, const WallThicknessParams& params = {});
+
+// Quick check: is minimum wall thickness >= required value?
+[[nodiscard]] bool check_min_wall_thickness(
+    const BrepModel& body, double min_required_mm);
+
+} // namespace vde::brep
+```
+
+## Undercut Detection
+
+### Manual Implementation in dfm_checker.cpp
+
+`checkUndercut()` (lines 427-456) performs:
+- Check the model for undercut features that prevent straight-pull mold ejection
+- Sample faces not visible from pull direction
+
+### Proposed VDE API
+
+```cpp
+// vde/brep/undercut_detection.h
+
+namespace vde::brep {
+
+struct PullDirection {
+    Vector3D direction;    // mold opening direction (typically Z+)
+    double tolerance = 0.01;  // angular tolerance (radians)
+};
+
+enum class UndercutType {
+    External,    // visible from outside, needs side-core/slider
+    Internal,    // enclosed pocket, needs lifter/collapsible core
+    Thread,      // threaded feature needs unscrewing core
+    SideHole     // hole perpendicular to pull direction
+};
+
+struct UndercutRegion {
+    std::vector<int> face_indices;
+    double area;
+    UndercutType type;
+    Point3D centroid;
+    bool requires_side_action;  // needs slider/lifter/hydraulic core
+};
+
+struct UndercutResult {
+    std::vector<UndercutRegion> regions;
+    bool is_moldable;               // true if no undercuts or all solvable
+    bool requires_split_line;       // parting line not planar
+    double external_undercut_area;  // total area requiring side cores
+    double internal_undercut_area;  // total area requiring lifters
+    std::string recommended_solution; // e.g., "Add 2 side cores + 1 lifter"
+};
+
+[[nodiscard]] UndercutResult detect_undercuts(
+    const BrepModel& body, const PullDirection& pull = {{0, 0, 1}});
+
+// For multi-direction mold analysis
+[[nodiscard]] UndercutResult detect_undercuts_multi_axis(
+    const BrepModel& body,
+    const std::vector<PullDirection>& axes);
+
+} // namespace vde::brep
+```
+
+## Impact on ViewDesign
+
+| Module | VDE Gap | Manual Workaround |
+|--------|---------|-------------------|
+| `dfm_checker.cpp` | No wall_thickness.h | Manual ray-casting against mesh |
+| `dfm_checker.cpp` | No undercut_detection.h | Face normal check against pull direction |
+| `mold_manager.cpp` | No undercut detection | Simplifies mold design analysis |
+| `additive_manager.cpp` | No wall thickness | Can't auto-detect printability issues |
+
+## Related
+- VDE-091: Mold design (parting line, core/cavity)
+- VDE-097: DFM analysis (this is the geometry backend for DFM rules)
+- VDE-111: vd_geom integration gaps